1. Field of the Invention
This invention relates to an off-lane alarm apparatus, and in particular to an off-lane alarm apparatus wherein by monitoring a road surface in front of or behind a car by means of a line camera which is also called an image sensor, an off-lane i.e. deviated state of the car from its traffic lane (white or yellow lane) is sensed, and an alarm is generated.
2. The Prior Art
In the prior art off-lane alarm apparatus known from the past for example, the Japanese Patent Application No. 4-170593, as shown in FIGS. 10A and 10B, a line camera 1 is mounted at a predetermined front center of a car 20 to shoot a lane WL as an image on a road surface 30. The image is quantized into a corresponding binary image indicating position data of the lane WL. From the position data of the car 20 and the lane WL, i.e. a distance therebetween, it is determined (judged or decided) that whether or not the car 20 lies in an off-lane state from the lane WL. When the determination indicates an off-lane state, an alarm is given to a driver.
For such an alarm determination or judgement, this off-lane alarm apparatus geometrically presets a positional relationship between the line camera, the car, and the road surface to settle a positional relationship between the car and the lane, at the stage of design.
Therefore, if the mounted position of the line camera misses the geometric relationship preset by the design, the geometric positional relationship between the line camera, the car, and the road surface will be broken, leading to an erroneous off-lane alarm determination.
Namely, if it is supposed that for the geometric positional relationship the optical axis of the line camera of the off-lane alarm apparatus coincides with the center line of the car, when the mounted position of the line camera is out of place an area on the road surface detected by the line camera becomes asymmetric. Therefore, the detection of such an off-lane state on the left and the right car sides as a distance between the lane and the side end of the car becomes zero.
This provides an earlier or delayed detection. In other words, although being not symmetric, the positions of the both side ends of the car are erroneously assumed in relation to the center of the car.
Therefore, it is necessary to carefully conduct a mounting work for the line camera. In the prior art, whether or not the mounted state of the line camera is out of place after mounting was checked by reproducing the off-lane state in actual running or by connecting a particular monitoring device to the line camera.
However, such a checking or pre-adjusting method has a large disadvantage in that pre-adjusting the line camera requires a considerable time and special preparation in the mounting process.
Accordingly, the inventor of the present invention has proposed, in Japanese Patent Application No. 5-35363, a method for adjusting a mounting angle of a line camera. The line camera is positioned at a predetermined front center of a car, and horizontal position data of a binary image of a marker are initially set as reference data when the marker is placed at a predetermined front point on the center line of the car. At the time of adjustments, the horizontal position data of the binary image of the marker as shot and the reference data are compared. According to the difference as a result of the comparison, an output condition of an adjusting mode lamp is changed so that the binary image and the reference data at the time of adjustment may coincide with each other. In this case, the detected area of the line camera is made symmetric.
However, in the Japanese Patent Application No. 5-35363, a method for adjusting a mounting angle of the line camera has been proposed so that a geometric relation prescribed at the stage of design may be satisfied. It has a large disadvantage due to process time restriction in view of a car mounting the off-lane alarm apparatus being inspected and adjusted on the manufacturing lines.